How to restart a non-responsive System Extension?

This is about macOS Big Sur.

Sometimes, our SysExt seems to get into a "degenerated" state. NETunnelProviderSession.startVPNTunnel(options:) returns without an error, but the call is not "arriving" at the SysExt (we've got logging there), and NETunnelProviderSession.sendProviderMessage(_:,responseHandler:) calls the handler with nil (again, no log on SysExt side about this). (The manager was queried with NETunnelProviderManager.loadAllFromPreferences.)

When this happens, sometimes it works by just trying those calls again, but often that doesn't work. During the betas, we found out that simply killing the SysExt with SIGQUIT would respawn the process and everything was fine again. However, that doesn't seem to work any more (or at least not reliably).

What are the options when the SysExt process is running but doesn't seem to respond? Would trying to get a fresh manager via NETunnelProviderManager.loadAllFromPreferences help in some way, or is there some way to restart the SysExt process? What can cause this in the first place, apart from us deadlocking some vital thread in the SysExt?
How to restart a non-responsive System Extension?
 
 
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